Does a Black Willow Tree Have Any Pest Problems?

Foliage Insects

• Foliage feeding insects such as the forest tent caterpillar and the larvae of the gypsy moth may feed on black willow, rolling or folding leaves, and sometimes creating silky nests. The National Forest Service comments that these insects may defoliate the tree and stunt growth, though they will rarely kill the tree. Prune and destroy heavily infested foliage, and scrap any visible egg masses off the bark. Drown eggs in a bucket of soapy water, and dump the water away from the tree.

Boring Insects

• Poplar and willow borers tunnel into bark and branches to lay their eggs, which then hatch and feed on tree stems. The paths left by the borers weaken the tree, leading to broken branches and dead portions of the tree. Some black willows may weaken and die from a severe infestation. Inserting and wiggling a wire around in the tunnels may help to puncture and kill larvae. You can also spray a borer insecticide into the hole, then seal it with putty or wax to keep the fumes inside.

Complications

• Some insects, and borers in particular, can spread diseases such as canker, scab and willow blight. Canker causes sunken lesions that can girdle the trunk and kill the tree. Canker and borer-related diseases are best prevented by taking proper care of the tree, according to the National Forest Service, as trees weakened by drought or neglect are more likely to attract pests. Black willow beetles can contribute to leaf rust, particularly on young seedlings.

Prevention

• Though black willow is a short-lived tree, efforts can be made to keep the tree healthy so that it is less likely to attract pests. Black willow is suitable for U.S. Department of Agriculture plant hardiness zones 2 to 8, where it prefers full sunlight. A native of the wetlands, black willow requires a soil that is consistently wet, even water logged or temporarily flooded. It grows well in saturated soils near streams, ponds and other bodies of water.